The present invention relates to seismic processing methods and finds a particularly advantageous application in 3D seismic prospecting methods that implement seismic data migration.
The need for higher quality imaging of seismic structures leads to the use of migration processing on seismic data prior to summing.
Unfortunately, a major problem encountered with seismic data migration lies in determining the travel time between a given position on the surface and a cube of positions at depth.
To obtain high quality migration processing, it is desirable to be able for high accuracy to be available on the calculated travel times.
However, although present processing makes highly satisfactory accuracy available, it suffers from the drawback of requiring a very large number of computation. The resulting computation time is particularly long.
For descriptions of various methods of solving the eikonal equation, reference can advantageously be made to the various following publications:
(1) Podvin P. and Lecompte I., 1991, Finite difference computation of travel times in very contrasted velocity models: a massively parallel approach and its associated tools: Geophys. J. Int., 105, 271-284;
(2) Schneider W., 1993, Robust, efficient upwind finite-difference travel time calculations in 3D: 1993 DEG Annual Meeting Expanded Abstracts;
(3) Fowler P., 1994, Finite-difference solutions of the 3D eikonal equation in spherical coordinates: 1994 SEG Annual Meeting Expanded Abstracts;
(4) Klimes L., 1996, Grid travel time tracing: second-order method for the first arrivals in smooth media, PAGEOPH: 148, 539-563,
(5) Geoltrain S. and Brac J., 1993; Can we image complex structures with first-arrival travel times?: Geophysics, 51, 1685-1688;
(6) Nichols D. E., 1996, maximum energy travel times calculated in the seismic frequency band: Geophysics, 61, 253-263;
(7) Kessler D. and Canales L., 1995, Mixed-grid solution of the 3D eikonal equation: 1995 SEG Annual Meeting Expanded Abstracts;
(8) Mendes M., Morgado L. and Buxo A., 1997, Interpolation sensitivity of the 3D ASI: Final Report EEC Joule contract JOU2-CT93-0321, 3D Asymptotic Seismic Imaging, 251-266; and
(9) Pica A., 1997, Maximum energy travel times and amplitudes calculated in a low frequency band: 1997 59th EAGE Conference Extended Abstracts.
An object of the invention is to propose processing that makes it possible to obtain high accuracy determinations in shorter times.